ethereum.forks.bpo3.state_tracker

State Tracking for Block Execution.

Track state changes on top of a read-only PreState. At block end, accumulated diffs feed into PreState.compute_state_root_and_trie_changes().

.. contents:: Table of Contents :backlinks: none :local:

Introduction

Replace the mutable State class with lightweight state trackers that record diffs. BlockState accumulates committed transaction changes across a block. TransactionState tracks in-flight changes within a single transaction and supports copy-on-write rollback.

BlockState

Accumulate committed transaction-level changes across a block.

Read chain: block writes -> pre_state.

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@final
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@dataclass
class BlockState:

pre_state

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    pre_state: PreState

account_writes

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    account_writes: Dict[Address, Optional[Account]] = field(
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        default_factory=dict
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    )

storage_writes

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    storage_writes: Dict[Address, Dict[Bytes32, U256]] = field(
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        default_factory=dict
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    )

code_writes

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    code_writes: Dict[Hash32, Bytes] = field(default_factory=dict)

TransactionState

Track in-flight state changes within a single transaction.

Read chain: tx writes -> block writes -> pre_state.

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@final
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@dataclass
class TransactionState:

parent

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    parent: BlockState

account_writes

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    account_writes: Dict[Address, Optional[Account]] = field(
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        default_factory=dict
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    )

storage_writes

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    storage_writes: Dict[Address, Dict[Bytes32, U256]] = field(
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        default_factory=dict
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    )

code_writes

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    code_writes: Dict[Hash32, Bytes] = field(default_factory=dict)

created_accounts

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    created_accounts: Set[Address] = field(default_factory=set)

transient_storage

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    transient_storage: Dict[Tuple[Address, Bytes32], U256] = field(
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        default_factory=dict
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    )

get_account_optional

Get the Account object at an address. Return None (rather than EMPTY_ACCOUNT) if there is no account at the address.

Parameters

tx_state : The transaction state. address : Address to look up.

Returns

account : Optional[Account] Account at address.

def get_account_optional(​tx_state: TransactionState, ​​address: Address​) -> Optional[Account]:
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    <snip>
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    if address in tx_state.account_writes:
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        return tx_state.account_writes[address]
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    if address in tx_state.parent.account_writes:
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        return tx_state.parent.account_writes[address]
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    return tx_state.parent.pre_state.get_account_optional(address)

get_account

Get the Account object at an address. Return EMPTY_ACCOUNT if there is no account at the address.

Use get_account_optional() if you care about the difference between a non-existent account and EMPTY_ACCOUNT.

Parameters

tx_state : The transaction state. address : Address to look up.

Returns

account : Account Account at address.

def get_account(​tx_state: TransactionState, ​​address: Address​) -> Account:
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    <snip>
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    account = get_account_optional(tx_state, address)
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    if account is None:
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        return EMPTY_ACCOUNT
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    else:
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        return account

get_code

Get the bytecode for a given code hash.

Read chain: tx code_writes -> block code_writes -> pre_state.

Parameters

tx_state : The transaction state. code_hash : Hash of the code to look up.

Returns

code : Bytes The bytecode.

def get_code(​tx_state: TransactionState, ​​code_hash: Hash32​) -> Bytes:
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    <snip>
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    if code_hash == EMPTY_CODE_HASH:
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        return b""
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    if code_hash in tx_state.code_writes:
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        return tx_state.code_writes[code_hash]
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    if code_hash in tx_state.parent.code_writes:
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        return tx_state.parent.code_writes[code_hash]
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    return tx_state.parent.pre_state.get_code(code_hash)

get_storage

Get a value at a storage key on an account. Return U256(0) if the storage key has not been set previously.

Parameters

tx_state : The transaction state. address : Address of the account. key : Key to look up.

Returns

value : U256 Value at the key.

def get_storage(​tx_state: TransactionState, ​​address: Address, ​​key: Bytes32​) -> U256:
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    <snip>
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    if address in tx_state.storage_writes:
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        if key in tx_state.storage_writes[address]:
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            return tx_state.storage_writes[address][key]
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    if address in tx_state.parent.storage_writes:
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        if key in tx_state.parent.storage_writes[address]:
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            return tx_state.parent.storage_writes[address][key]
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    return tx_state.parent.pre_state.get_storage(address, key)

get_storage_original

Get the original value in a storage slot i.e. the value before the current transaction began. Read from block-level writes, then pre_state. Return U256(0) for accounts created in the current transaction.

Parameters

tx_state : The transaction state. address : Address of the account to read the value from. key : Key of the storage slot.

def get_storage_original(​tx_state: TransactionState, ​​address: Address, ​​key: Bytes32​) -> U256:
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    <snip>
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    if address in tx_state.created_accounts:
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        return U256(0)
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    if address in tx_state.parent.storage_writes:
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        if key in tx_state.parent.storage_writes[address]:
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            return tx_state.parent.storage_writes[address][key]
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    return tx_state.parent.pre_state.get_storage(address, key)

get_transient_storage

Get a value at a storage key on an account from transient storage. Return U256(0) if the storage key has not been set previously.

Parameters

tx_state : The transaction state. address : Address of the account. key : Key to look up.

Returns

value : U256 Value at the key.

def get_transient_storage(​tx_state: TransactionState, ​​address: Address, ​​key: Bytes32​) -> U256:
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    <snip>
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    return tx_state.transient_storage.get((address, key), U256(0))

account_exists

Check if an account exists in the state trie.

Parameters

tx_state : The transaction state. address : Address of the account that needs to be checked.

Returns

account_exists : bool True if account exists in the state trie, False otherwise.

def account_exists(​tx_state: TransactionState, ​​address: Address​) -> bool:
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    <snip>
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    return get_account_optional(tx_state, address) is not None

account_deployable

Check if an account's code can be written to.

def account_deployable(​tx_state: TransactionState, ​​address: Address​) -> bool:
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    <snip>
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    account = get_account(tx_state, address)
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    if account.nonce != Uint(0) or account.code_hash != EMPTY_CODE_HASH:
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        return False
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    if account_has_storage(tx_state, address):
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        return False
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    return True

account_has_storage

Check if an account has storage.

Parameters

tx_state : The transaction state. address : Address of the account that needs to be checked.

Returns

has_storage : bool True if the account has storage, False otherwise.

def account_has_storage(​tx_state: TransactionState, ​​address: Address​) -> bool:
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    <snip>
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    if tx_state.storage_writes.get(address):
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        return True
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    if tx_state.parent.storage_writes.get(address):
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        return True
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    return tx_state.parent.pre_state.account_has_storage(address)

account_exists_and_is_empty

Check if an account exists and has zero nonce, empty code and zero balance.

Parameters

tx_state : The transaction state. address : Address of the account that needs to be checked.

Returns

exists_and_is_empty : bool True if an account exists and has zero nonce, empty code and zero balance, False otherwise.

def account_exists_and_is_empty(​tx_state: TransactionState, ​​address: Address​) -> bool:
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    <snip>
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    account = get_account_optional(tx_state, address)
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    return (
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        account is not None
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        and account.nonce == Uint(0)
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        and account.code_hash == EMPTY_CODE_HASH
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        and account.balance == 0
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    )

is_account_alive

Check whether an account is both in the state and non-empty.

Parameters

tx_state : The transaction state. address : Address of the account that needs to be checked.

Returns

is_alive : bool True if the account is alive.

def is_account_alive(​tx_state: TransactionState, ​​address: Address​) -> bool:
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    <snip>
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    account = get_account_optional(tx_state, address)
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    return account is not None and account != EMPTY_ACCOUNT

set_account

Set the Account object at an address. Setting to None deletes the account (but not its storage, see destroy_account()).

Parameters

tx_state : The transaction state. address : Address to set. account : Account to set at address.

def set_account(​tx_state: TransactionState, ​​address: Address, ​​account: Optional[Account]​) -> None:
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    <snip>
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    tx_state.account_writes[address] = account

set_storage

Set a value at a storage key on an account.

Parameters

tx_state : The transaction state. address : Address of the account. key : Key to set. value : Value to set at the key.

def set_storage(​tx_state: TransactionState, ​​address: Address, ​​key: Bytes32, ​​value: U256​) -> None:
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    <snip>
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    assert get_account_optional(tx_state, address) is not None
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    if address not in tx_state.storage_writes:
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        tx_state.storage_writes[address] = {}
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    tx_state.storage_writes[address][key] = value

destroy_account

Completely remove the account at address and all of its storage.

This function is made available exclusively for the SELFDESTRUCT opcode. It is expected that SELFDESTRUCT will be disabled in a future hardfork and this function will be removed. Only supports same transaction destruction.

Parameters

tx_state : The transaction state. address : Address of account to destroy.

def destroy_account(​tx_state: TransactionState, ​​address: Address​) -> None:
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    <snip>
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    destroy_storage(tx_state, address)
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    set_account(tx_state, address, None)

destroy_storage

Completely remove the storage at address.

Only supports same transaction destruction.

Parameters

tx_state : The transaction state. address : Address of account whose storage is to be deleted.

def destroy_storage(​tx_state: TransactionState, ​​address: Address​) -> None:
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    <snip>
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    if address in tx_state.storage_writes:
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        del tx_state.storage_writes[address]

mark_account_created

Mark an account as having been created in the current transaction. This information is used by get_storage_original() to handle an obscure edgecase, and to respect the constraints added to SELFDESTRUCT by EIP-6780.

The marker is not removed even if the account creation reverts. Since the account cannot have had code prior to its creation and can't call get_storage_original(), this is harmless.

Parameters

tx_state : The transaction state. address : Address of the account that has been created.

def mark_account_created(​tx_state: TransactionState, ​​address: Address​) -> None:
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    <snip>
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    tx_state.created_accounts.add(address)

set_transient_storage

Set a value at a storage key on an account in transient storage.

Parameters

tx_state : The transaction state. address : Address of the account. key : Key to set. value : Value to set at the key.

def set_transient_storage(​tx_state: TransactionState, ​​address: Address, ​​key: Bytes32, ​​value: U256​) -> None:
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    <snip>
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    if value == U256(0):
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        tx_state.transient_storage.pop((address, key), None)
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    else:
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        tx_state.transient_storage[(address, key)] = value

modify_state

Modify an Account in the state. If, after modification, the account exists and has zero nonce, empty code, and zero balance, it is destroyed.

def modify_state(​tx_state: TransactionState, ​​address: Address, ​​f: Callable[[Account], None]​) -> None:
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    <snip>
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    set_account(tx_state, address, modify(get_account(tx_state, address), f))
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    if account_exists_and_is_empty(tx_state, address):
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        destroy_account(tx_state, address)

move_ether

Move funds between accounts.

Parameters

tx_state : The transaction state. sender_address : Address of the sender. recipient_address : Address of the recipient. amount : The amount to transfer.

def move_ether(​tx_state: TransactionState, ​​sender_address: Address, ​​recipient_address: Address, ​​amount: U256​) -> None:
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    <snip>
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    def reduce_sender_balance(sender: Account) -> None:
532
        if sender.balance < amount:
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            raise AssertionError
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        sender.balance -= amount
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    def increase_recipient_balance(recipient: Account) -> None:
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        recipient.balance += amount
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    modify_state(tx_state, sender_address, reduce_sender_balance)
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    modify_state(tx_state, recipient_address, increase_recipient_balance)

create_ether

Add newly created ether to an account.

Parameters

tx_state : The transaction state. address : Address of the account to which ether is added. amount : The amount of ether to be added to the account of interest.

def create_ether(​tx_state: TransactionState, ​​address: Address, ​​amount: U256​) -> None:
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    <snip>
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    def increase_balance(account: Account) -> None:
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        account.balance += amount
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    modify_state(tx_state, address, increase_balance)

set_account_balance

Set the balance of an account.

Parameters

tx_state : The transaction state. address : Address of the account whose balance needs to be set. amount : The amount that needs to be set in the balance.

def set_account_balance(​tx_state: TransactionState, ​​address: Address, ​​amount: U256​) -> None:
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    <snip>
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    def set_balance(account: Account) -> None:
584
        account.balance = amount
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    modify_state(tx_state, address, set_balance)

increment_nonce

Increment the nonce of an account.

Parameters

tx_state : The transaction state. address : Address of the account whose nonce needs to be incremented.

def increment_nonce(​tx_state: TransactionState, ​​address: Address​) -> None:
590
    <snip>
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    def increase_nonce(sender: Account) -> None:
603
        sender.nonce += Uint(1)
604
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    modify_state(tx_state, address, increase_nonce)

set_code

Set Account code.

Parameters

tx_state : The transaction state. address : Address of the account whose code needs to be updated. code : The bytecode that needs to be set.

def set_code(​tx_state: TransactionState, ​​address: Address, ​​code: Bytes​) -> None:
611
    <snip>
624
    code_hash = keccak256(code)
625
    if code_hash != EMPTY_CODE_HASH:
626
        tx_state.code_writes[code_hash] = code
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    def write_code_hash(sender: Account) -> None:
629
        sender.code_hash = code_hash
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    modify_state(tx_state, address, write_code_hash)

copy_tx_state

Create a snapshot of the transaction state for rollback.

Deep-copy writes and transient storage. The parent reference and created_accounts are shared (not rolled back).

Parameters

tx_state : The transaction state to snapshot.

Returns

snapshot : TransactionState A copy of the transaction state.

def copy_tx_state(​tx_state: TransactionState​) -> TransactionState:
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    <snip>
655
    return TransactionState(
656
        parent=tx_state.parent,
657
        account_writes=dict(tx_state.account_writes),
658
        storage_writes={
659
            addr: dict(slots)
660
            for addr, slots in tx_state.storage_writes.items()
661
        },
662
        code_writes=dict(tx_state.code_writes),
663
        created_accounts=tx_state.created_accounts,
664
        transient_storage=dict(tx_state.transient_storage),
665
    )

restore_tx_state

Restore transaction state from a snapshot (rollback on failure).

Parameters

tx_state : The transaction state to restore. snapshot : The snapshot to restore from.

def restore_tx_state(​tx_state: TransactionState, ​​snapshot: TransactionState​) -> None:
671
    <snip>
682
    tx_state.account_writes = snapshot.account_writes
683
    tx_state.storage_writes = snapshot.storage_writes
684
    tx_state.code_writes = snapshot.code_writes
685
    tx_state.transient_storage = snapshot.transient_storage

incorporate_tx_into_block

Merge transaction writes into the block state and clear for reuse.

Parameters

tx_state : The transaction state to commit.

def incorporate_tx_into_block(​tx_state: TransactionState​) -> None:
692
    <snip>
701
    block = tx_state.parent
702
703
    for address, account in tx_state.account_writes.items():
704
        block.account_writes[address] = account
705
706
    for address, slots in tx_state.storage_writes.items():
707
        if address not in block.storage_writes:
708
            block.storage_writes[address] = {}
709
        block.storage_writes[address].update(slots)
710
711
    block.code_writes.update(tx_state.code_writes)
712
713
    tx_state.account_writes.clear()
714
    tx_state.storage_writes.clear()
715
    tx_state.code_writes.clear()
716
    tx_state.created_accounts.clear()
717
    tx_state.transient_storage.clear()

extract_block_diff

Extract account, storage, and code diff from the block state.

Parameters

block_state : The block state.

Returns

diff : BlockDiff Account, storage, and code changes accumulated during block execution.

def extract_block_diff(​block_state: BlockState​) -> BlockDiff:
721
    <snip>
735
    return BlockDiff(
736
        account_changes=block_state.account_writes,
737
        storage_changes=block_state.storage_writes,
738
        code_changes=block_state.code_writes,
739
    )